Making underground storage caverns



P. G. CARPENTER MAKING UNDERGROUND STORAGE CAVERNS Original Filed June16, 1952 A 7' TORNEYS Aug. l, 1961 United States Patent ice PatentedAug. l, 1961 I This invention relates to an improved method for makingunderground storage caverns. In one of its aspects this inventionrelates to a method for protecting the roof of an underground storagecavern in a salt formation while forming the cavern by dissolving outthe salt with water.

This application is a continuation of my application Serial No. 293,868,iiled June 16, 1952.

A perennial problem of petroleum refiners during the summer months isthe storage of excess by-products which have no market, such as fuel oiland liquefied petroleum gas such as liquefied propane, liquefied butaneand mixtures of the two. In an effort to alleviate this storage problemthere has recently been developed a method for storing liquefiedpetroleum products in underground storage caverns formed by drilling toa salt formation and dissolving out a portion of the salt to form acavern. 'I'his method has great potential in these days of allocation ofcritical materials such as steel. The advantages of underground storageover above-ground storage include: (l) lower costs, both initial andmaintenance (underground storage has been estimated lto cost as much assix times less than steel tankage); (2) savings in ground space; (3)savings in the use of steel; (4) elimination of above-ground operationalhazards; and (5) bomb proof protection for liquefied petroleum gasmixtures.

So far as is known no attempts have been made to apply the principlesherein involved to formations other than salt. However, many shalesreadily disintegrate in water and such formation may be employed. Also,in some cases it may be feasible to dissolve space out of massivelimestone with hydrochloric acid. The extensive occurrence of saltdeposits believed suitable to this method of storage is another factorin favor of its increasing use.

In the usual case there is a layer of hard anhydrite above the saltformation and when drilling the well casting pipe is cemented in thishard anhydrite layer. .The borehole is then extended into the saltformation and fresh water is circulated down through the tubing todissolve out part of the salt thus forming a cavern. In those cases thehard anhydrite layer forms the roof of the resultingcavern and theproblem of caving of the roof or dissolving out the foot of the casingis not encountered. In many instances, however, where there is no hardanhydrite layer, such as in a salt dome, or in other instances Y Wherethe formation above the salt formation is subject to caving, casing pipeis cemented directly into the salt bed to a lengthwhich will result in asalt layer above the cavernproof ofsuflicient thickness which will notcave. In this instance it is necessary to protect the foot of the casingand the roof of the resulting cavern from the dissolving action ofthesolvent employed. `One cause of eating the roof is the fact that saltwater is heavier than fresh Water. Thus the fresh water will tend torise to the top of the cavern and thus Vdissolves the roof away fasterthan the bottom or walls of the cavern. It is to the solution of thisproblem andthe prevention of contaminationof liquefied petroleumproducts subsequently stored in the resulting cavernsthat the presentinvention is directed. f Y

.An object of this invention is to provide an improved method` ofVmaking an underground storage cavern.

AIt isanother object of this invention to provide a method forprotecting the roof of an underground storage cavern in a salt formationwhile forming the cavern by dissolving out the salt with Water, andpreventing unnecessary contamination of the material subsequently storedin the cavern.

Further and additional objects of this invention will be apparent fromthe accompanying descriptions and drawing.

FIGURE 1 of the drawing is a vertical cross-sectional view partly inelevation showing one embodiment of my invention.

FIGURE 2 of the drawing is a similar view showing another embodiment ofmy invention.

It is, of course, important that the finished underground storage cavernbe free from any leaks through which the product subsequently storedtherein may be los-t. In making caverns in salt formations to be usedfor the storage of liquefied petroleum gas extra care is necessary tolmake certain there are no leaks in the roof of the cavern when, becauseof the nature of the strata immediately above the salt, viz., containingharmful fractures or is soft and crumbly and subject to caving, leaksare possible. The obvious solution to such a problem is to form thecavern completely in the salt formation, maintaining a layer of saltover the cavern thick enough to insure suicient support, cementingcasing pipe directly into the salt. However, the problem then arises ofprotecting the roof of the cavern around the foot of the bore hole fromthe dissolving action of the solvent employed, to prevent leaks fromdeveloping around the cemented casing pipe into a faulty upper formationand caving of the remainder of the cavern roof. lt has been suggested inthe art of mining salt by dissolving it from an underground formationwith water, to protect the roof of the resulting cavern around the footof the bore hole by maintaining (1) a layer of compressed air, or (2) anon-solvent such as petroleum or shale oil between the roof of thecavern and the solvent. However, when, according to the latter method,diesel oil was employed in forming a salt cavern for storing liquefiedpetroleum gas the LPG subsequently stored therein was contaminated andrequired a reprocessing before it could be used. If the former method isemployed it is necessary for best results to use two strings v of pipebesides the casing pipe and employ extremely high air pressure toprotect the roof of the cavern. I have now discovered that the problemshereinbefore described can be concomitantly and economically solved bymaintaining as a separate phase liquefied petroleum gas between the roofof the cavern and the solvent employed.

Referring now to FIGURE l of the drawing, one embodiment of my inventionemploying a single string of pipe is illustrated. Bore hole 10 isdrilled into salt for- :mation 11 to a depth dependent upon the desiredthickness of salt to be maintained between the cavern and the adjacentupper strata. Of course, in those instances where the strata immediatelyabove the salt layer in which the pipe. The depth of this recess ordepression is dependenty cavern is to be formed is a hard impervioussubstance suitable to form the roof of the cavern, such as hardanhydrite, the method of this invention is unnecessary. Casing pipe 12.is set into the salt formation and cemented therein to give it a firmfooting. The bore hole can then -be deepened to any ldesired depth intothe salt formation.

the roof of the cavern. This can be described as a recessV 14 in thecavern roof adjacent `to the foot of the casing upon such factors as thethickness of the salt to the upper Strata, the ultimate size of thecavern, and length of cementing of casing pipe. Three to ten feet couldbe set as an optimum depth. However, since it Vwould Vbe difficult todetermine the extent of the recess, it can be reasonably assumed thatafter the cavern has reached a capacity of yaround 500 barrels, formedas hereinbefore described, that a recess of the desired size will exist.At this stage inthe formationl of the cavern the circulation of freshwater is stopped and liqueiicd petroleum gas is spotted in the recess inthe cavern roof, thus forming a protective layer'between the roof of thecavern and the fresh water solvent. This spotting operation can beaccomplished either by passing the LPG down casing pipe 12, or down pipe13. In the latter instancerin order to get better spotting, it isdesirable toV raise pipe 13 so that its lower end is lapproximatelylevel with the foot of the casing pipe, and then pass LPG down to thecavern. The LPG is generally passed down as a liquid; however, it can bepumped down as a gas under pressure such that it wil-l be a liquid uponreaching the cavern. After the LPG is spotted it is preferred that thecirculation be reversed; that is, as shown in FIGURE l, passing freshwater down the casing pipe and returning the resulting salt solution tothe surface via pipe 13. This reverse circulation is best suited tomaintain the less dense LPG as a separate phase on top of the watersolvent and between the cavern roof. However, the circulation can bevaried occasionally to facilitate better dissolving action by the water.The rate of circulation of water canbe controlled in conventional Ways,such as by regulating pumps or valves. The amount vof LPG initiallyspotted will depend on the size of the cavern.- In some instances it maybe necessary to add LPG as the size of the cavern increases, or becausesome has been lost in the course of water circulation. Because of thedepth of the cavern, viz., 250 to 3000 feet generally, and because theLPG will he trapped in recess 14 under pressure, no appreciable amountwill be lost due to evaporation. Y

Referring to FIG. 2 of the drawing, this embodiment of my inventionemploys two concentric strings of pipe Within the casing pipe. Bore hole2G' is drilled into salt formation 2'1 and casing 22 cemented therein.The hole is then continueddeeper into the formation and two concentricstrings of pipe 23 Vand 24 are lowered to the salt formation.In-starting the cavern the lower end of outer pipe Z3 is approximatelylevel with the foot of casing pipe 22 and the lower end of innerV pipe24 extends farther into the hole. Fresh water is passed down throughouter pipe 23 and saltsolution returned to the surface via inner pipe24. The rate of circulation of water can be controlled by such meansV asregulating pumps or valves. As the cavern enlarges outer pipe 23 islowered and at the same time suliicient LPG is passed down to the cavernthrough casing Vpipe 22 to form a layer on top of the water and thusprotect the roof of the cavern from the dissolving action of the water.By operating in this manner the roof of the lresulting cavern has aslope which increases its resistance to caving. The circulation can bereversed occasionally. There mayor may not be a recess formed in theVcavern roof adjacent to the foot of casing pipe 22 as hereinbeforedescribed, depending upon how soonafter circulation -is started Vthatouter pipe 23 is lowered and LPG passed down. When using twoV strings ofpipe there is no need to trap the LPG inthe roof ofthe cavern since itcan be readily'rrraintained there via the casing pipe. The method of thepresent invention when employing two strings of pipe for circulatingwater is -a definite improveV ment over the use of compressed air inthat the probability appreciate that modilications can be made withoutdeparting from the spirit and scope of the invention.

I claim:

l. A method of making an underground storage cavern for liquefiedpetroleum gas, comprising the steps of circulating through anunderground formation a liquid which is a solvent for said form-ation toform a recess in the roof of said formation, spotting liquefiedpetroleum gas in that theV waterrwill attack the roof ,of the cavern ismuch i less and further, it is possible to store LPG while actuallyforming the cavern.

While this invention has been described in terms of itsYpreferred"emhodiments those skilled in the art will readily saidrecess, continuing the circulation of said solvent liquid whereby anunderground 4cavern is leached out of said formation, and shielding theroof of said cavern from said solvent during the leaching step bymaintaining aY layer of liquefied petroleum gas between the surface ofsaid solvent and said cavern roof.

2. A method of making an underground storage cavern for liquefliedpetroleum gas, comprising drilling-into a water soluble salt formation,cementing casing pipe into said formation, circulating fresh water tosaid formation through one conduit means, removing salt from saidformation as solution through another conduit means until suicient salthas been dissolved from around the cemented casing foot in the cavernroof to form a recess in said roof around said foot, spotting liqueedpetroleum gas in said recess, and maintaining liquefied petroleum gasduring the enlargement of said cavern as a separate phase between thecavern roof and the water solvent whereby said cavern roof is protectedfrom. further dissolution and contamination of liquefied petroleum gassubsequently stored in said cavern is prevented.

3. A method of making an underground storage cavern for liquefiedpetroleum gas comprising drilling into a water soluble salt formation,cementing casing pipe into said formation, circulating fresh water tosaid formation through an inner string of pipe, removing salt from saidformation as solution through the casing pipe until sumcient salt hasbeen dissolved from around the cemented casing foot in the cavern roofto form a recess in said roof around said foot, spotting liquefiedpetroleum gas in said recess, reversing the circulation and then whileenlarging by circulating more water maintaining said liquefied petroleumgas as a separate phase between the roof of the cavern and the watersolvent whereby 4the roof of the cavern is protected from furtherdissolution and contamination of liquefied petroleum gas subsequentlystored in said cavern is prevented.

4. The method according to claim 3 where in said recess is hom three toten feet in depth.

5. A method of making an underground storage cavern for liquefiedpetroleum gas by drilling into a water soluble salt formation, cementingcasing into said formation, po# sitioning first and second strings ofpipe within said casing so that the lower end of said first string ofpipe is approximatelyrlevel with the foot of said casing and the lowerend of said second string of pipe is lower than the foot of said casing,circulating freshwater through one of said strings of pipe, removingsalt from said formation in solution through the other of said pipes,gradually lowering said first pipe string from the foot of the casing asformation of said cavern proceeds, passing liqueled petroleum gas downto said cavern and then While enlarging by circulating more watermaintaining saidjliquelied petroleum gas as a separate phase between thecavern roof and the water solvent whereby said cavern roof isprotectedfrom the dissolving action of solvent and contamination ofliqueed petroleum gas subsequently stored Y' in said cavern isprevented.

cavern is leached out of said formation, shielding theroof ofsaid cavernfrom said solvent during theleaching operation-by maintaining a layer ofliquefied petroleum Vgas u between the `surface of said solvent and saidcavern roof,

and filling said cavern at the conclusion of the lleaching operationwith liquefied petroleum gas.

7. A method for storing liquefied petroleum gas in an undergroundstorage cavern, comprising circulating an aqueous liquid from thesurface of the earth through a water soluble underground formation andback to the surface to dissolve out a cavern in said formation,maintaining a layer of liquefied petroleum gas between the cavern roofand the surface of said solvent during preparation of said cavern,whereby said cavern roof is protected from dissolution, and filling saidcavern at the conclusion of the leaching operation with liquefiedpetroleum gas Which is maintained in air-tight storage therein.

8. A method for storing liquefied petroleum gas in an undergroundstorage cavern, comprising drilling to a suitable underground formation,cementing casing pipe into said formation, passing a liquid to saidformation and forming a cavern therein by the action of said liquid onsaid formation and removing part of said formation admixed with saidliquid, concomitantly protecting the cavern roof from the action of saidliquid and preventing contamination of liquefied petroleum gassubsequently stored in said cavern by maintaining said liquefiedpetroleum gas as a separate phase between said cavern roof and saidliquid, and filling said cavern at the conclusion of the leachingoperation with liquefied petroleum gas which is maintained in airtightstorage therein.

9. A method for storing liquefied petroleum gas in an undergroundstorage cavern, comprising drilling into a water soluble salt formation,cementing casing pipe into said formation, circulating 4fresh water tosaid formation through one conduit means, removing salt from saidformation as solution through another conduit means until sufficientsalt has been dissolved, maintaining liquefied petroleum gas during theenlargement of said cavern as a separate phase between the cavern roofand the water solvent whereby said cavern roof is protected from furtherdissolution and contamination of liquefied petroleum gas subsequentlystored in said cavern is prevented, and filling said cavern at theconclusion of the leaching operationrwith liquefied petroleum gas whichis maintained in air-tight storage therein.

10. A method for storing liquefied petroleum gas in an undergroundstorage cavern, comprising drilling into a water soluble salt formation,cementing casing pipe into said formation, circulating fresh water tosaid formation through one conduit means, removing the salt from saidformation as solution through another conduit means until. suicient salthas been dissolved from around the cemented casing foot in the cavernroof to form a recess in said roof around said foot, spotting liquefiedpetroleum gas in said recess, maintaining liquefied petroleum gas duringthe enlargement of said cavern as a separate phase between the cavernroof and the water solvent whereby said cavern roof is protected fromfurther dissolution and contamination of liquefied petroleum gassubsequently Stored in said cavern is prevented, and filling said cavernat the conclusion of the leaching, operation with liquefied petroleumgas which is maintained in air-tight storage therein.

11. A method for storing liquefied petroleum gas in an undergroundstorage cavern without contaminating said gas with other hydrocarbonmaterial, comprising the steps of drilling into a Water soluble saltformation, cementing casing pipe into said formation, circulating freshwater to said formation through an inner string of pipe, removing saltfrom said lformation as solution through said casing pipe untilsuiiicient salt has been dissolved from around the cemented casing footin the cavern roof to form a recess in said roof around said foot,spotting liquefied petroleum gas in said recess, reversing thecirculation and then while enlarging said cavern by circulating morefresh water maintaining said liquefied petroleum gas as a separate phasebetween the roof of said cavern and the water solvent whereby the roofof the cavern is protected from further dissolution, substantially llingthe cavern with liquefied petroleum gas by introducing the same throughsaid casing pipe into said cavern to displace said salt solution throughsaid inner string of pipe, storing the thus introduced liquefiedpetroleum gas in said cavern, and removing the stored liquefiedpetroleum gas from said cavernas needed through said casing pipe bydisplacing said stored liquefied petroleum gas with said salt solutionintroduced in said cavern through said inner string of pipe.

12. A method for storing liquefied petroleum gas in an undergroundstorage cavern Without contaminating said gas with other hydrocarbonmaterial, comprising the steps of drilling into a water soluble saltformation, cementing Ithe casing pipe into said formation, circulatingfresh water through -the first of two strings of pipe within said casingpipe, removing salt from said formation in solution through the other ofsaid pipes, the base of the said first pipe being near the bottom of theresulting cavern and 'the base of the other pipe being gradually loweredfrom the foot of the casing pipe as the formation of the cavernproceeds, passing suiiicient liquefied petroleum gas down to said cavernthrough said casing pipe while said other pipe is Abeing graduallylowered whereby the liquefied petroleum gas forms a separate phasebetween the roof of the cavern and the Water solvent, continuing theformation of the cavern by dissolving said salt with said fresh water,substantially lling the cavern with liquefied petroleum gas byintroducing the same through said casing pipe into said cavern todisplace said salt solution through said first string of pipe, storingthe thus introduced liquefied pertoleum gas in said cavern, and removingthe stored liquefied petroleum gas from said cavern as needed throughsaid casing pipe by displacing said stored liquefied petroleum gas insaid cavern, and removing the stored said cavern through said firststring of pipe.

13. A method for storing liquefied petroleum gas in an undergroundstorage cavern without contaminating said gas with other hydrocarbonmaterial, comprising the steps of drilling into a water soluble saltformation, cementing the casing pipe into said formation, circulatingfresh water through the first of two strings of pipe Within said casingpipe, removing salt from said formation in solution through the other ofsaid pipes, the base of the said first pipe being near the bottom of theresulting cavern and the base of the other pipe being gradually loweredfrom the foot of the casing pipe as the formation of -the cavernproceeds, occasionally reversing the circulation of said fresh water andsaid salt solution, passing sufficient liquefied petroleum gas down tosaid cavern through said casing pipe while said other pipe is beinggradually lowered whereby the liquefied petroleum gas forms a separatephase between the roof of the cavern and the water solvent, continuingthe formati-on of the cavern by dissolving said salt with said freshwater, substantially filling the cavern with liquefied petroleum gas byintroducing the same through said casing pipe into said cavern todisplace said salt solution through said first string of pipe, storingthe thus introduced liquefied petroleum gas in said cavern, and removingthe stored liquefied petroleum gas from said cavern as needed throughsaid casing pipe by displacing said stored liquefied petroleum gas withsaid salt solution introduced in said cavern through said first stringof pipe.

14. A method for storing liquefied petroleum gas in an undergroundstorage cavern without contaminating said gas with other hydrocarbonmaterial, comprising the steps of drilling into a Water soluble saltformation, cementing the casing pipe into said formation, circulatingfresh water through the outer of twoconcentric strings of pipe withinsaid casing pipe, removing salt from said formation in solution throughthev inner o-f said pipes, the base of the inner pipe being near thebottom of the resulting cavern and the base of the outer pipe beinggradually lowered from the foot of the casing pipe as the formation ofthe cavern proceeds-occasionally reversing the circulation ofv saidfresh water and said salt solution, passing suflicient liquefiedpetroleum gas down to said cavern through said casing pipe While saidouter pipe is being gradually lowered whereby the liquefied petroleumgas forms a separate phase between the root` of the cavern and the Watersolvent, continuing the formation of the cavern by dissolving said saltwith said fresh Water, substantially iilling the cavern with liquefiedpetroleum gas by introducing the same through said casing pipe into saidcavern to displace said salt solution through said inner string of pipe,storing Ithe thus introduced liquefied petroleum gas in said cavern, andremoving the stored liquefied petroleum gas from said cavern as neededthrough said casing pipe by displacing said sto-red liquefied petroleumgas -with said salt solution introduced in said cavern through saidinner string of pipe.

15. A method for storing liquefied petroleum gas in an undergroundstorage cavern without contaminating said gas with other hydrocarbonmaterial, comprising the steps of drilling into a water soluble saltformation, cementing the casing pipe into said formation, circulatingfresh water through the inner of two concentric strings of pipe Withinsaid casing pipe, removing salt from said `formation in solution throughthe outer of said pipes, the base of the inner pipe being near thebottom of the resulting cavern land the base of the outer pipe beinggradually lowered from the foot of the casing pipe as the formation ofthe cavern proceeds, occasionally reversing the circulation of saidfresh Water and said salt solution, passing sufficient liqueed petroleumgas down to said cavern through said casing pipe While said inner pipeis being gradually lowered whereby the liquefied petroleum gas forms'aseparate phase between the roof of the cavern and the water solvent,continuing the formation of the cavern by dissolving said salt with saidfresh water, substantially iilling the cavern with liquefied -petroleumgas by in-troducing the same through said casing pipe into said cavernto displace said salt solution through said outer string of pipe,storing the thus introduced liqueed petroleum gas in said cavern, andremoving the stored liquefied petroleum gas from said cavern as neededthrough said casing pipe byrdisplacing said stored liqueed petroleum gaswith said salt solution introduced in said cavern through said outerstring of pipe.

16. An improved structure forY the storage of liquid petroleum gascomprising, in-combination, a sealed underground cavern formed entirelywithin a water soluble earth formation, a rlirst vertical conduitconnecting said 3 3 y cavern with the surface of the earth, the lowerend of said `iirst conduit extending to a point near the base of saidcavern, a second conduit extending into said cavern but terminatingatits lower end portion at a'point adjacent the roof of said cavern atwhich point said roof denes a recess, means for admitting andwithdrawing fluids to and from said conduits at the upper ends thereof,an aqueous solution occupying the lower portion of said cavern, and alayer of liquid petroleum gas occupying the space between said aqueoussolution and said roof, including said recess, whereby said root isprotected from the solvent action of said aqueous solution.

17. A structure for the storage of liquid petroleum gas comprising incombination, a sealed underground cavern formed entirely within a watersoluble earth formation, a lrst vertical conduit connecting said cavernWith the surface of the earth, the lower end of said conduit extendingto a point near the base of the cavern, a second conduit annularlyspacedly surrounding the iirst conduit but terminating `at its lower endportion at a point adjacent the root of the cavern, a recess inthecavern roof, said lower end por-tion of the second conduit opening intosaid recess and extending below the upper surface thereof, a fluid tightseal between the recess Iand said second conduit, means `.for admittingand withdrawing uids to and Vfrom Ysaid conduits at the upper endsthereof, 'an aqueous solution oceuping the lower portion of the cavernyand a layer of a liquid lighter than and immiscible with the aqueoussolution and inert to the earth formation occupying the recess and thespace between the aqueous solution and cavern roof whereby the cavernroof is protected from the solvent action of the aqueous solution.

18. A structure for the storage of liquid petroleum gas according toclaim 17 wherein said liquid lighter than and immiscible with theaqueous solution is liquid petroleum gas.

References Cited in the le of this patent UNITED STATES PATENTS Oil andGas Journal of Aug. 17, 1950, pp. 59 and

